dhclient works on boot but not later

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FloydATC
Posts: 1
Joined: 2007/06/16 15:24:56

dhclient works on boot but not later

Post by FloydATC » 2007/06/16 16:12:18

I have been struggling with this problem for a good while now and I'm getting nowhere... I have a linux router running CentOS, with ethernet devices eth0 and eth1.

eth0 is connected to a DSL modem and configured with DHCP
eth1 is connected to my LAN, using the 10.0.0.0 network

When the box boots up, dhclient runs ok and everything works:

Jun 10 05:16:11 athena dhclient: DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 2
Jun 10 05:16:11 athena dhclient: receive_packet failed on eth0: Network is down
Jun 10 05:16:11 athena dhclient: DHCPOFFER from #.#.#.1
Jun 10 05:16:16 athena dhclient: DHCPREQUEST on eth0 to 255.255.255.255 port 67
Jun 10 05:16:16 athena dhclient: DHCPACK from #.#.#.1
Jun 10 05:16:16 athena NET: /sbin/dhclient-script : updated /etc/resolv.conf
Jun 10 05:16:16 athena dhclient: bound to #.#.#.253 -- renewal in 1298 seconds.

So far, so good. A little later, as expected, the lease is renewed:

Jun 10 05:37:54 athena dhclient: DHCPREQUEST on eth0 to #.#.#.1 port 67
Jun 10 05:37:54 athena dhclient: DHCPACK from #.#.#.1
Jun 10 05:37:54 athena dhclient: bound to #.#.#.253 -- renewal in 1396 seconds.

We're still good... until all of a sudden:

Jun 10 17:17:24 athena dhclient: DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 2
Jun 10 17:17:24 athena dhclient: receive_packet failed on eth0: Network is down
Jun 10 17:17:26 athena dhclient: No DHCPOFFERS received.
Jun 10 17:17:26 athena dhclient: No working leases in persistent database - sleeping.

I can try over and over and over and over again, it won't work. Not until I reboot, and then everything works again.
I don't understand why it all of a sudden goes back into DHCPDISCOVER, when there's a perfectly good lease available for renewal, and I certainly don't understand why the DHCP server broadcast all of a sudden won't get through.

I have been on the phone with the ppl at the other end of the DSL, we go way back and they know what they're doing. He can see the DHCPOFFER getting sent from their end, but using tcpdump at my end I get nothing. Normally this would indicate a faulty DSL modem or connection, but then... a reboot fixes everything.

Oh and yes, I am using iptables. Have tried without it, and I have also made the following exception:
iptables -A INPUT -p udp --sport 67:68 --dport 67:68 -j ACCEPT

Any ideas please??

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